September 13, 509 BC is the traditional date of the dedication of the Temple of Jupiter in Rome. 509 BC, according to tradition, is also the year in which the last king, known as Tarquinius Superbus, "Tarquinius the Haughty," was exiled from the city and the Roman Republic was established. To us it would have looked much more like a very exclusive oligarchy than a real republic, but it had some advantages over the monarchy, and over the Empire which would come centuries later. Leaders were elected, albeit by a small group of aristocrats, and they served short terms. Typically two co-rulers, consuls, were elected yearly. if they were unsuitable -- to this small group of aristocrats -- then it was only a short wait until their terms expired, they didn't have to be assassinated. "Regnatum Romae ab condita urbe ad liberatam annos ducentos quadraginta quattuor." writes Livy at the end of Book 1 of his history of Rome. "The rule of Romans by kings (lasted) two hundred and forty-four years from the founding of the city until their liberation."
244 years, from another traditional date, that of the founding of Rome in 753 BC, to 509. The story the ancient Romans told of the founding of their city sounds very much like a legend: Romulus and Remus, the twin brothers and founders of the city, were raised by a she-wolf. While the boundaries of the city were being laid out, Remus jumped playfully back and forth over the boundary-line, and for this lack of respect for the awesome solemnness of the occasion, Romulus killed him. None of it sounds very true to life. By the time we get to Tarquinius the Haughty and the beginning of the republic, the traditional story has started to sound much less legendary and much more life-like, but it's hard to know what parts may be true. After Rome was sacked by Gauls led by Brennius in -- or around -- 390 BC, the chronology seems much more solid, there seems to be now something which we can call a reliable historical record, with the consuls listed for each year and so forth. Maybe there were similar records before the attack by Brennius, in the form of inscriptions, monuments and written records, which the Gauls either destroyed or carried off. Or perhaps the Romans only started keeping meticulous records after this invasion -- perhaps in part as a psychological defense mechanism against the trauma of the destruction of their city. Keeping exact dates for historical events, whether these dates are reliable or not, can help citizens to feel that their state is solid and secure.
If Americans feel inclined to chuckle at the Romans for so carefully preserving, even in the sophisticated age of Cicero and Caesar, Augustus and Livy, an early history which may have been mostly myth, with Romulus and Remus, and insisting that they knew the exact day when an important temple was dedicated, I would urge them to ponder things like George Washington shopping down a cherry tree and and throwing a silver dollar across the Potomac. We're not so different from them.